Yes, you can buy the Swiss Travel Pass at the airport but it is more convenient to buy it online. Price wise there is no difference. The Swiss Railways webshop at www.swissrailways.com/ en sells it for the same price and lets you print the pass at home. That saves you from waiting at the ticket office, and also you will have a PDF file as a backup in case you would damage or lose the pass. Other retailers may charge a bit less or a bit more, depending on exchange rates. You'll find all options listed at myswissalps.com/swisst ravelpass/price.